The present invention relates to wood-fueled boilers that are capable of using multiple fuels (e.g. wood, fuel oil and/or natural or propane gas) and, in particular, to a boiler outfitted with a gas/oil burner assembly having an independently controlled, air control valve mounted between the firebox and burner nozzle.
Wood and biomass fueled boilers necessarily include air controls to vary the draft or amount of combustion air admitted to the firebox. Uncontrolled drafts are to be avoided, if optimized control is to be obtained over combustion.
Where the boiler is operable with multiple fuel sources, separate nozzle and burner assemblies are typically coupled to the firebox to admit heated combustion gases. The burner is typically controlled independently to assure continuing boiler operation, even if the wood fire is allowed to burnout. Operational problems can arise, however, from extraneous and uncontrolled airflow through the burner assembly that is not coordinated with the draft control to the wood fire.
The present improved boiler was developed to accommodate the foregoing need and appropriately control and/or isolate airflow through an oil/gas burner assembly relative to the firebox. An injector tube that contains an oil/gas nozzle and through which combustion gasses flow includes a butterfly valve to control airflow through the tube. The valve is normally closed, unless the burner is operational, to isolate the firebox from the ambient environment and unregulated air.
It is a primary object of the invention to provide a multi-fuel boiler with a combustion air-controlled oil/gas burner assembly.
It is further object of the invention to provide a boiler, primarily fueled by wood or other solid fuels, with a secondary burner assembly fueled by oil, gas and other non-solid fuels and having a separately controlled, independent source of combustion air that can be isolated from the firebox.
It is a further object of the invention to provide an injector tube that contains a fuel nozzle and a butterfly valve and which valve operates to isolate combustion air at the secondary burner assembly from the firebox when the burner isn""t operating (i.e. wood fire only) to control extraneous airflow to the firebox.
It is further object of the invention to provide multiple modes of secondary burner operation to backup, supplement or replace wood combustion and during which the valve is open, for example, a) automatic secondary fuel backup, b) timed xe2x80x9cstartupxe2x80x9dxe2x80x94secondary fuel burner fired for timed period at startup of wood fire, and c) oil/gas only. In the latter mode, the wood fire damper is closed.
The foregoing objects, advantages and distinctions of the invention are obtained in a presently preferred, butterfly controlled burner assembly. The assembly provides a conventional oil/gas burner and nozzle assembly that is fitted to an injector tube. A butterfly valve is supported in the injector tube, forward of the nozzle, and a motorized linkage directs valve operation. When the burner is non-operational, the valve isolates the oil/gas burner from the boiler to prevent drafts that can interfere with the regulation of the primary combustion air to the firebox.